1. Field of the Invention
The present invention relates to a current sensor that measures the magnitude of current. Particularly, the present invention relates to a current sensor in which degradation in measurement accuracy is suppressed.
2. Description of the Related Art
In fields such as a motor driving technique in an electric vehicle or a hybrid vehicle, relatively high current is involved, and for this application, a current sensor capable of contactlessly measuring a high current is required. In addition, as the current sensor, a current sensor having a method of detecting a change in magnetic field caused by a current to be measured using a magnetic sensor is used in practice. In addition, the current sensor using the magnetic sensor has a problem of degradation in measurement accuracy due to an effect of a disturbance magnetic field, and thus methods of suppressing this are suggested.
As the method of suppressing degradation in measurement accuracy due to an effect of a disturbance magnetic field, for example, a configuration in which a differential in output signals of two magnetic sensors is acquired is suggested (for example, refer to U.S. Pat. No. 6,642,705). In this configuration, in the output signals of the two magnetic sensors, an effect of a magnetic field formed by a current to be measured is expressed as a reversed phase, and the effect of the disturbance magnetic field is expressed as the same phase. Therefore, by acquiring the differential, the effect of the disturbance magnetic field may be removed. In addition, since the output signals of the magnetic sensors are analog signals, in the corresponding method, all correction processes including differential operation are performed on the basis of the analog signals.
On the other hand, a method of performing partial processes on the basis of digital signals other than performing all correction processes on the basis of analog signals is suggested (for example, see Pamphlet of International Publication WO 2008/047428). In this method, after acquiring a differential with a differential amplifier, an analog differential value is converted into a digital signal using an analog-to-digital converter, and the subsequent processes are performed.
As described above, in the case where all the correction processes are performed using analog signals, an adjustment scheme such as adjustment of variable resistance or laser trimming for resistances needs to be used in order to enhance the correction accuracy. However, this scheme is only a onetime scheme, and re-adjustment is difficult. In addition, this scheme is disadvantageous in terms of cost. On the other hand, in the method described in Pamphlet of International Publication WO 2008/047428, such problems may be solved to some extent. However, there is a problem in that appropriate correction is difficult in a case where noise is left in the analog differential value and the like.